Dll tricks

As i understand you writing windows application.
In this case the best solution is to use Named file mapping.
Refer MSDN about this:
==========8<===========
Sharing Files and Memory
File mapping can be used to share a file or memory between two or more processes. To share a file or memory, all of the processes must use the name or the handle of the same file-mapping object.

To share a file, the first process creates or opens a file by using the CreateFile function. Next, it creates a file-mapping object by using the CreateFileMapping function, specifying the file handle and a name for the file-mapping object. The names of event, semaphore, mutex, and file-mapping objects share the same name space. Therefore, the CreateFileMapping and OpenFileMapping functions fail if they specify a name that is in use by an object of another type.

To share memory that is not associated with a file, a process must use the CreateFileMapping function and specify (HANDLE)0xFFFFFFFF as the hfile parameter instead of an existing file handle. The corresponding file-mapping object accesses memory backed by the system paging file. You must specify a size greater than zero when you specify an hfile of (HANDLE)0xFFFFFFFF in a call to CreateFileMapping.

The easiest way for other processes to obtain a handle of the file-mapping object created by the first process is to use the OpenFileMapping function and specify the object's name. This is referred to as named shared memory. If the file-mapping object does not have a name, the process must obtain a handle to it through inheritance or duplication. For more information on inheritance and duplication, see Inheritance.

Processes that share files or memory must create file views by using the MapViewOfFile or MapViewOfFileEx function. They must coordinate their access using semaphores, mutexes, events, or some other mutual exclusion technique. For more information, see Synchronization.

A shared file-mapping object will not be destroyed until all processes that use it close their handles to it by using the CloseHandle function.
==========8<===========

You might also consider

#pragma comment(linker,"/SECTION:.SharedData,RWS")
#pragma data_seg (".SharedData")    
int g_iMySharedStuff = 0;
#pragma data_seg ()

but you should control access to it using a Semaphore.

I accept GGRUNDY's technique but how do I share any Object of a class in the same manner

Only static object can be shared in such way.

kosolobov can you give me a small example please

kosolobov can you give me a small example please

My comment was about GGRUNDY's variant and it will look like before

#pragma comment(linker,"/SECTION:.SharedData,RWS")
#pragma data_seg (".SharedData")    

CMyClass object;

#pragma data_seg ()

the only limitation - class must not allocate memory inside constructor.

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I am doing the same way as said by kosolobov and ggrundy, but it is still not working, I am giving my code below. Plz find any mistake I made
// proctestdll.cpp : Defines the entry point for the DLL application.
//

#include "stdafx.h"
#include "stdio.h"

#ifdef __cplusplus
#define DE extern "C" _declspec(dllexport)
#else
#define DE _declspec(dllexport)
#endif
class  A{
public:
          int z;

     A(){
          z=0;
     }
     void setz(int v){
          z+=v;
     }
     int getz(){
          return z;
     }
};



BOOL APIENTRY DllMain( HANDLE hModule,
                       DWORD  ul_reason_for_call,
                       LPVOID lpReserved
                          )
{
      int i=10;
          if(ul_reason_for_call==DLL_PROCESS_ATTACH){
          ::MessageBox(NULL,"PROCESS_ATTACH","MSG",16);
          printf("i= %d\n",i);
          i++;
          }

     else if(ul_reason_for_call==DLL_THREAD_ATTACH)
               ::MessageBox(NULL,"THREAD_ATTACH","MSG",16);

     else if(ul_reason_for_call==DLL_THREAD_DETACH)
               ::MessageBox(NULL,"THREAD_DETACH","MSG",16);

     else if(ul_reason_for_call==DLL_PROCESS_DETACH)
               ::MessageBox(NULL,"PROCESS_DETACH","MSG",16);

    return TRUE;
}
#pragma data_seg("SHARED")
static A a;
int i=0;
#pragma data_seg()
#pragma comment(linker, "/section:SHARED,RWS")



DE void func(int* p){
     
     printf("address of p %u  value %d\n",p,*p);
     printf("address of i in func %u : %d\n",&i,i);
     ::MessageBox(NULL,"msg","MSG",16);
     i+=20;
     printf("address of i in func %u : %d\n",&i,i);

     ::MessageBox(NULL,"msg","MSG",16);
}

DE void setfunc(int k){
     a.setz (k);
}

DE int getfunc(){
     return a.getz();
}

Hmm from memory....
a class in global shared memory can't have a constructor.
Try taking the constructor out and see what happens.
(Don't worry the global memory is initialized to zero anyway).

In the code above I am calling setfunc and getfunc from processes but no where in any process I am getting the updated(as set by any other process) value of z.I have also removed the constructor

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Finalized today.